The invention is particularly applicable for inductively heating spaced main bearings of a crankshaft and it will be described with particular reference thereto; however, the invention has much broader applications and may be used for inductively heating cylindrical surfaces on elongated metal workpieces of various types. The cylindrical surfaces are generally concentric with the rotational axis of the elongated workpiece, except for variations caused by bowing of the workpiece and manufacturing tolerances thereof.
In the manufacture of crankshafts, of the type used in internal combustion engines, a large number of axially spaced cylindrical surfaces are employed. These surfaces are machined to the desired size and thereafter hardened. This hardening operation is generally performed by inductively heating the cylindrical surfaces as the crankshaft is rotated and then quench hardening the inductivity heated surfaces. The cylindrical surfaces form axially spaced bearing surfaces for operation of the crankshaft. A variety of machines have been developed for inductively heating and then quench hardening the various spaced cylindrical surfaces of the crankshaft. These machines generally involve an inductor placed in a fixed spaced relationship with a given surface and energized while the crankshaft is rotated. This arrangement progressively heats the cylindrical surface by induction heating. Thereafter, quenching liquid can be directed through the inductor against the heated surface for quench hardening the same. When the offset pin surfaces are being inductively heated and then quench hardened, the inductor must orbit as the crankshaft is being rotated. Special machines have been developed for this purpose. One of the machines is disclosed in prior U.S. Pat. No. 3,174,738, which is incorporated by reference herein for background. In this prior patent, a plurality of inductors are positioned on the pins of a crankshaft which is then rotated. Pressure is maintained on the inductor by a biasing arrangement which is counterbalanced to reduce the amount of pressure applied against the heated surface by locators riding on the inductors. This type of machine is adapted for heat treating the pin surfaces of a rotating crankshaft; however, such a machine is relatively expensive and complex for inductively heating the main bearing surfaces of a crankshaft, which bearing surfaces are generally concentric with the rotational axis of the crankshaft. The present invention relates to an improved device for heating the main bearings of a crankshaft, which device is less expensive than the complicated machine illustrated in the prior patent discussed above and is more efficient in operation.